Frequency selective surfaces can be provided to selectively reduce reflections from incident electromagnetic radiation. Such surfaces may be employed in signature management applications to reduce radar returns. These applications are typically employed within the radio frequency portion of the electromagnetic spectrum.
The use of multiple frequency selective surfaces disposed above a ground plane, for radio frequency applications, is described in U.S. Pat. No. 6,538,596 to Gilbert. Gilbert relies on the multiple frequency selective surfaces providing a virtual continuous quarter wavelength effect. Such a quarter wavelength effect results in a canceling of the fields at the surface of the structure. Thus, although individual layers may be spaced at less than one-quarter wavelength (e.g., λ/12 or λ/16), Gilbert relies on macroscopic (far field) superposition of resonances from three of four sheets, such that the resulting structure thickness will be on the order of one-quarter wavelength.
The use of electrically conductive surface elements to create a tunable absorptive structures/devices is described in U.S. Pat. No. 7,956,793 to Puscasu et al. Puscasu uses a single conductive layer with a plurality of surface elements to create a tunable primary resonance related to the size of the surface elements. A less efficient secondary resonance is defined by the center-to-center spacing of the plurality of surface elements. The resonances of Puscasu are created in the visible and infrared portion of the electromagnetic spectrum.